Motor starters



Feb. 3, 1959 P. M. cHRlsTENsl-:N 2,872,548

MOTOR STARTERS Filed Dec. l, 1955 2 Sheets-Sheet 2 INVENTOR PAUL @HQ/S TEA/ssn ATTORNEY United States Patent O MTOR STARTERS Paul M. Christensen, West range, N. Il., assignor to Federal Pacino Electric Company, 'a corporation of Delaware Application December 1, 1955, Serial No. 5565310 23 Claims. (Cl. 200--116) The present invention relates to overload-responsive devices, for protecting or indicating overload in electric circuits. v

A common form of overload-responsive device contains a thermal element that is heated by the load current, passed either directly through the thermal element or through a heater close to the thermal element. An indicator or a pair of contacts or both are arranged to be tripped under control of the thermal element when the load current produces excessive heating.

The controlled contacts are in series with the load in thermal circuit breakers. In overload relays, the controlled contacts do not carry the load current. Relay contacts are connected to control a tripping solenoid for the main load-carrying contacts, where the solenoid and main contacts ordinarily do not form part of the relay.

This invention has broad application to all such thermal overload protective devices, and to overload indicating or warning devices, etc. When tripped, the device may shift an indicator, or operate a contact, or both; and in the case of contacts, usually an overload will cause closing, although opening of the contacts is occasionally required. The term over-load responsive element is used herein to signify an indicator or a trip element or a pair of contacts that are opened or closed in response to overload. The invention has particular application to overload relays, as will be seen.

Overload relays have heretofore been made either compensated for ambient temperature variations, o1' uncompensated. Where the relay is used close to the protected load, the relay and the load are exposed to the same temperatures. It is usually desirable to trip the relay when excessive heating of both develops as a result of combined loading and ambient temperature conditions. In a low ambient location, a higher load level can be tolerated than in a high ambient location. A thermally compensated relay may be undesirable under such conditions. On the other hand, the relay may be located remote from the protected load so that the relay and the load may be exposed to widely different temperatures. Thus, a relay in a hot location would trip far below the maximum safe level where the protected load is in a cool location. Conversely, a relay in a cool location would not give proper protection to a motor, for example, in a hot location. To correct for this, thermally compensated relays are sometimes demanded.

An object of the present invention is to avoid the necessity of producing both types of overload-responsive devices for the different needs, types with ambient compensation and other omitting ambient compensation. A feature of the invention resides in the provision of an overload device which is adaptable selectively to function as a normal uncompensated device or to function with ambient temperature compensation.

A variety of sizes of overload devices are required for different electrical loads. Each size may be made adjustable over a'range of overload levels, with obvious advantages. l

A further object of the present invention resides in the provision of an overload-responsive device that may set selectively either to provide ambient compensation or to avoid ambient compensation, and in either setting to provide for an adjustable level of tripping.V A more detailed feature of the invention resides in the provision of means preventing easy change from compensated to uncompensated operation, particularly without interfering with adjustability of the tripping load level.

The illustrative embodiment of the invention described in detail below is an overload relay for a three-phase motor control. In this relay there are a pair of contacts, and a plurality of bimetals control the contacts. A separate bimetal is included for each protected connection to the load. Where there are multiple connections to a polyphase motor, there ordinarily will be one bimetal for each phase. The current in each protected connection or phase is arranged to heat its related bimetal. The mechanism is such that if any of the phases carries an overload current or if any of the phases should fail, the contacts are tripped open.

ln this illustrative relay the mechanism linking the bimetals to the contacts incorporates an adjustable device that determines the level at which overload tripping of the contacts takes place; and this adjustable device is either fixed mechanically in a definite position initially set, or, the adjustment is made variable in dependence on the ambient temperature.

in the illustrative relay, the selective setting of the de- `ice to achieve ambient temperature compensation or to avoid such compensation is further made adjustable to any load within a range of tripping levels. As a result, operation of the contacts under control of the load-respensive bimetals can be set to any desired level Within a range of levels, and the adjustment can be made subject to ambient temperature compensation or independent thereof, as may be desired by the user. Moreover, the novel illustrative relay incorporates a single selector that determines trippingcurrent level and it also determines whether or not the relay is to be ambient compensated.

The nature of the invention and further features of novelty will be apparent from the following detailed disclosure of an illustrative embodiment of the invention shown in the accompanying drawings forming part of the disclosure.

In the drawings:

Fig. 1 is a plan view of a novel motor starter embodying features of the invention, with the top removed and the enclosure shown in cross-section, to reveal portions of the internal mechanism;

Fig. 2 is a cross-section of the motor starter along the line 2 2 in Fig. l;

Fig. 3 is a cross-section of the motor starter in Figs. 1 and 2 in the plane 3 3 of Fig. 2;

Fig. 4 is a fragmentary cross-section in the plane 4-4 of Fig. 3;

Fig. 5 is a fragmentary cross-section of the motor starter in the previous iigures as viewed from the left side of Fig. 3 with the enclosure wall removed to reveal a portion of the enclosed mechanism;

Fig. 6 is a vertical cross-section in the plane 6-6 of Fig. 2;

Fig. 7 is a fragmentary view in the plane 7-7 in Fig. 2;

Fig. 7a is a fragmentary cross-section in the plane 7a-7a of Fig. 2;

Fig. 8 is a View similar to Fig. 7 with the parts in a modified configuration; and

Fig. 8a is a fragmentary cross-section similar to Fig. 7a with the parts in a modified conguration.

Referring now to Figs. 1 to 6 inclusive, the basic mechanism of the novel three-phase overload protection relay there shown will be described.

The overload relay involves a two-part enclosure formed of insulating material, including a base 12 and a side-and-top cover 14, thecover being slidable'upward for removal. Four pairs of external terminals 16 project from the bottom of the enclosure,.as plug-in connections for the motor starter. To these terminals various electrical'connections are made within the enclosure.

' Three'bimetals 18 are shown, each within a separate chamber in the enclosure. VA heater 29 of resistance wire is wound about each bimetal 18 and suitably protected by electrical and thermal insulation. Current will follow through the resistor from one terminal 29a to the opposite terminal Zb to heat the bimetal so as to cause deflection. Bimetal 18 is supported on a connector ,that is joined to one external terminal 16. Heater terminal 20a is connected via connector 24 to a second external terminal 16. A circuit extends from one external terminal16, via connector 22, bimetal 1S, heater terminal 20h, heater 20, terminal 20a and connector 24 to the yopposite terminal 16.

. VWhere a three-phase motor is to be protected, for example, a heater 20 is interposed as a series connection to the three-phase power supply, a separate heater element being available for each of the three phases.

v The left-hand side of these bimetals is the high-expansion side, `so that during the proper operation all three `binletals will dellect moderately to the right in Figs. 1 and 2. In the event of overload all three 'bimetals will deflect to the right through a prominent distance so as .to cause overload tripping as will be described; and in the event of phase failure one of the bimetals 1S will, upon cooling, shift to the left and in this condition will also cause tripping of the contacts, as will be seen.

The contact mechanism which is controlled by the bimetals 18 as just described, is shown in Figs. 3 to 5 inclusive. The mechanical coupling from the bimetals to this contact mechanism will be detailed later.

An adjustably mounted contact 26 is shown engaged by movable contact 28. The contacts are closed when so engaged. Movable contact 2S is carried by a contact arm 30 pivoted in V-slots 32a of metal frame 32 that is fixed suitably in the housing and electrically joined to one external terminal 16. From the left-hand plug-in terminal 16 in Fig. 3 the circuit .through the contacts extends through frame 32, contact arm 3d, contacts .ES and 26, and to the right-hand plug-in terminal 16.

A tension spring 34 biases vcontact arm-3l3 upward against its V-seat 32a. The upper end of spring 3d is joined to a trip member 36 supported on pivot 36a on frame 32.

As seen in Figures 3, 4 and 5 a vertical slide or reset member 33 is provided having a lower end portion 33a which is engageable by contact arm 30 in two positions A and B represented in dotted lines in Fig.: 3. -With slide 38 elevated as shown in full lines in Fig.,3, it is possible to shift' trip member 36 clockwise so as to move tension spring 34 past pivot 32aV and over center. Arm 30 then snaps into position A of Fig. V3. The proportions are such that, after returnV of member 36 to the full line position shown, the upper end of tension spring 3d remains at the left of pivot 32a.

When stop 38a is lowered to the dotted-line position in Fig.- 3 and with the contacts closed, contact arm 3i? swings to position B when trip member 36 moves spring 34 over center. Thereafter, with the mechanism appropriately proportioned, return of member 36 to theV fullline position shown will cause automatic reclosing of contacts 26, 2S. VWith member 38 in-the dotted-line position the contacts open when trip member 36 swings clockwise; and the contacts reclose automatically upon return of member 36 to its normalV full'line position in Fig. 3. The contacts remain open when once opened by trip member 36 if reset member 38 is in the Vfull-line position of Fig. 3. When member 38 is depressed the contacts 4 re-close. Member 38 is returned to the full-line position by spring 39. Stop 41 limits the upward travel of member 3S. When it is found desirable `to provide for automatic re-closing of the contacts, reset member is held down. This is done by `shifting detent 43 from the position shown into position overlying the depressed slide 38.

The mechanism enabling bimetals 18 to operate trip member 36 may now be described with particular reference to Figs. i to 3. A pair of strips at), 42 of insulation are slidable in passages 44 formed in the walls separating the bimetal chambers from each other and from the chamber at the left (Figs. l and 2) containing the contact mechanism and from the chamber at the right, containing other mechanism later to 'be described. Bell crank d6 has a pivot 4S to slide 40 and another pivot 3@ to slide 4t2; and the left-hand arm 46a of member do engages trip member 36. The upper, free end of each bimetal 1S normally bears tiatwise against the lefthand edge 46a of a respective notch in slide dll, and against the right-hand side 42a of a respective notch in slide d2. it is apparent that shifting of the free ends of bimetals 13 due to the moderate heating of normal loads in all phases will simply cause portion da of bell cransF 6 to slide along the surface of trip member 36 without moving that trip member. However, if slide fr were arrested while bimetals 18 or any of them continued t0 dellect further to the right, slide 42 would shift to the right and swing member @d to operate trip member 35 in the direction to open the contacts. Also, if all of the bimetals are shifted to the right of their positions shown in the drawings by normal-load heating, and if one of the `coils should Vfail to receive heating current, its related bimetal 13 would then shift to `the left relative to the other bimetals. Slide d2 would be held in position by the normally heated bimetals 13, whereas the cool bimetal 18 in shifting to the left would shift slide do and pivot d8 to the left, so as to swing bell crank 46 in the direction to trip the contacts. Both overload tripping and phase failure tripping is thus accomplished by the same tripping mechanism.

Phase Vfailure is a term that applies technically to interruption of power to one phase of a polyphase alternating current load such as a motor with power continuing to be fed to one or more other phases. The same term applies more broadly to a load energized through multiple protected connections. For example, it is possible for an internal ground to develop in a single-phase motor which would bypass one of the protected connections. This would simulate phase failure, and it is desirable that the protective device should trip under such conditions even though no overload may exist. The term phase failure or phase protection is used to apply to the condition of multiple load connections, each of whichhas protective bimetal or the like, and where tripping occurs in the event of prominent imbalance developing among the connections or phases. v i. -thas been noted that overloading in the protective device causes all of the bimetals 18 to shift to the right in Figs. l and 2, and that this causes operation of bell crank d6 and trip member 36 when slide dit is arrested and slide d2 continues to shift to the right in consequence of *heating of bimetals 13. The stop mechanism which arrests slide-dt) or against which slide 40 reacts to produce tripping in response to `an overload is disposed at the righthand extremity of the unit in Figs. 1 andi, and this mechanism is also illustrated in Figs. 6, 7, 7a, S and 8a. Stop member 52 has laterally extending pivots 54 that are received'in recesses'd molded in the enclosure portion 12. A tension spring 58 engages horizontally extending arm 66 of member 52 so as to bias stop member 52 clockwise in Fig. 2. Thisl is in the direction away from Slide A-tl. Y f j A selector 62V is disposed at kthe upper right-hand portion of the enclosure Vas shown in Fig. 2 and serves to ase/ams limit the clockwise swing of member 52 about pivots 54 under the influence of spring 58. Member 52 has a rst stop portion 64 which cooperates with a first selector portion 62a. Stop member 52 also carries a bimetal 66 whose upper end 66a is adjacent stop portion 64 that cooperates with selector portion 62b.

Selector 62 has a pivot shaft 68 extending through the end wall of the enclosure for rotating the selector into either of two settings selectively, so that either stop portion 64 or portion 66a of bimetal 66 will arrest the clockwise swing of stop member `62. Both stop portions 64 and 66a are below shaft 68 and selector portions 62a and 6211 are on opposite sides of this shaft, so that either selector portion but not both will be elfective at any one time. As seen in the drawings selector portions 62a and 62h are contoured-so as to resemble cams; and they function as cams in adjusting stop member 52 through a range from the extreme left position illustrated in Fig. 2 to the extreme right position represented by the dotted lines in Fig. 2. By virtue of this adjustment the current level at which tripping occurs can be set at will. By virtue of the selective reaction means including the two diierent stop portions 64 and 66a which cooperate with the selective portions of selector 62, the overload tripping is made to occur either with or without compensation for variations in ambient temperature. Secured to shaft 68 is a knob 70 for enabling adjustment of selector 62 into any desired adjusted position.

A screw 72 extends through knob 70 parallel to shaft 68 and cooperates with a pair of fixed stops 74 and 76 which project from the end of the enclosure. When screw 72 is fully inserted, the knob is prevented from rotating beyond a limited range. Screw 72 is effective to limit the adjustment of selector 62 either through a lirst range, where stop portion 64 cooperates with selector portion 62a (Figs. 8 and 8a) or through second range, in which stop portion 66a cooperates with selector portion 62b (Figs. 7 and 7a). The user is free to adjust the overload tripping level by changing the setting of knob 70. However, screw 72 inhibits change of selection from ambient compensating. to non-compensating or vice versa.

In order to further inhibit the user from changing from one to the other type of operation after selection has already been made, the head of screw 72 is formed with abutment surfaces 72a which enables a screwdriver to drive the screw in but the screw-head has sloping surfaces that extend `away from abutment surfaces 72a so that reverse loperation of a screwdriver in an attempt to remove the screw to change the knob setting is all but impossible. Before screw 72 is in place, selector 62 can be manipulated to select either type of operation, compensated or uncompensated. With the screw fully inserted, however, selector 62 can be adjusted to determine the tripping level.

The cylindrical face of knob '70 has calibration markings 7S corresponding with the tripping levels established by the various points along contoured selector portions 62u and 6215, and the top of the casing has an index mark pointing to the particular tripping level in effect for each angular position of knob 7d. The calibration is ordinarily in terms of amperes although any other units may be employed. The ratings represented by these caiibration es are conventionally established under standardized conditions, including a standard ambient temperature. Therefore it is understood, particularly with reference to the uncompensated calibration, that the rated load levels shown `by the calibration markings represent response levels at the ambient temperature prevailing during calibration, and the actual loads at which response should occur at other operating ambient temperatures may be expected to depart from the calibrated values to an extent that depends in part on the difference between the standard and the actual operating ambient temperatures. 'As shown in the drawing, the markings for-the ambient compensated portion of the knob contrast in color or otherwise with the markings for the.

non-compensated range.

It is evident from the foregoing that an unitary motor control relay has been described in detail in which provision is made for selective setting either for ambient compensationior to avoid ambient compensation. Further in either setting provision is made for adjusting the maximum load level at which tripping occurs. These features are provided in a motor control relay in which phase failure prevention is also provided, the whole being effectively integrated. It is apparent however that certain of the novel features included in this illustrative embodiment may be employed without sacrificing the advantages of the others. Thus Vfor example while screw 72 which inhibits the change of selection from ambient compensating to non-compensating is undoubtedly of great importance in someapplications this inhibiting feature may be omitted without sacrificing the features identified with the release of the selector mechanism. Further the selector concept undoubtedly has advantage not only in the present application where multiple load connections are effective in controlling the relay, but also in less demanding circumstances, as where no phase failure provision is made. Various modifications and applications of the novel features of this illustrative embodiment of the invention will occur to those skilled in the art. Consequently, it is appropriate that the invention be broadly construed in manner consistent with its full spirit and scope.

I claim:

l. A circuit protector, including a pair of contacts and control mechanism therefor including a current-responsive thermal element effective to cause operation of the contacts automatically in response to overload, an ambient temperature compensating element, and selective means settable in one manner to interpose said compensating element in said mechanism to impose the inliuence of said compensating element on said control mechanism, said selective means also 'being settable in another manner to exclude said compensating element from said control mechanism and to render said control mechanism itself effective to cooperate said contacts in response to overload.

2. A circuit protector, including an enclosure containing a pair of contacts and control mechanism therefor including a current-responsive thermal element eiective to cause operation of the contacts automatically in response to overload, an ambient temperature compensating element, and selective means accessible externallyof said enclosure and settable in one manner to interpose said compensating element in said mechanism to impose the inuence of said compensating element on said control mechanism, said selective means also being settable in another manner to exclude said compensating element from said control mechanism and to render said control mechanism itself effective to operate said contacts in response to overload.

3. A load-responsive device, including an enclosure containing a controlled element and a current-respon-` sive thermal element in control relation to a controlled element, an ambient' temperature compensating element, and selective means accessible from the exterior of said enclosure and settable in one manner to interpose said compensating element in said control relation to impose the inuence of said compensating element on said control relation and said selective means also being settable in another manner to exclude said compensating element from said control relation and to render said current responsive thermal element itself effective to operate said controlled element in response to electric current.

4. A load-responsive device, including a controlled element and a current-responsive thermal element in control relation to said controlled element, an ambient temperature compensating element, and selective means settable in one manner to interpose said compensating ele-.

erases element and a current-responsive thermal c. .nent in control relation to the controlled element, electrical means causing heating of said current-responsive thermal element'as a function of load, an ambient temperature compensating element, and selective means settable in one manner to resolve the temperature response of said co npensating element and said thermalelement and to apply the resultant to said controlled element, and said selective means also being settable in another manner in which said control relation of theA controlled element and the current-responsive element is maintained but in which said compensating element is prevented from modifying said control,` said selective means being adapted to provide substantially equal rated load response of the loadresponsive device both in the temperature compensating and uncompensated settings of said selective means.

6. A loadfresponsive device, including a pair of contacts and operating mechanism therefor including a control bimetal effective to cause operation of the contacts, means causing heating said bimetal as a function of electrical loading, an ambient temperature compensating bimetal, and selective means settable to establish cooperation between said bimetals in causing said operation of the contacts and settable di-fferentlv to reestablish control of said controlled element by said control bimetal and to prevent said compensating bimetal from affecting the control by said control bimetal, said selective means being adapted to provide equal rated response of said contacts in both temperature compensating and uncompensated settings of said selective means.

7. A load-responsive device, including a controlled element and a control bimetal in control relation to said element, electrical means for heating said bimetal as a function of electrical loading, an ambient Ytemperature compensating bin-letal, and selective means settable to establish cooperation between said bmetals in controlling said element and settable differently to prevent said com pensating bimetal trom affecting the control by said control bimetal, said selective meansjbeing adapted to provide equal rated response of said controlled element in both said different'settings of said selective means.

8. A load-responsive device, including an enclosureV containing a controlled element and a control bimctal in controfrejlation to' said element, electrical means for heating said bimetal as a function of electrical loading, an ambient temperature compensating bimetal, and selective means accessible externally of `said enclosure and settable to establish cooperation between said bimetals in controlling saidV element and settable differently to prevent said compensating bimetal from affecting the controlV by said control bimetal, said selective means being adapted to provide equal rated response of said controlled element in both said different settings of said selective means.

9. Acircuit protective device, including an enclosure containing a pair of contacts and operating mechanism therefor including a control bimetal effective to cause operation of the contacts, electrical means for heating said bimetal as a function of electrical loading, an ambient temperature compensating bimetal, externally accessibleselective means settable to'establish cooperation between said bimetals in causing operation of the contacts and settable differently to prevent ysaid compensating bimetal from affecting the control by said control bimetal, said selective meansbeingY adapted Yto Yprovide equal rated response of said contacts for both said different settings of said selective means, and means operable to inhibit change of setting of said selective means after initial Vsetting thereof in one manner or the other,

l0. A load-responsivedevice, including an enclosure, a controlled element, a control bimetal iu control relation to said controlled element and electrical means for heating said bimetal as a function of electrical loading, an ambient temperature compensating bimetal, externally accessible selective means settable to cause cooperation bctween said birnetals in controlling said element and settable differently to maintain control of said controlled element by said control bimetal and to prevent said compensating bimetal from affecting the control by said control bimetal, said selective means being adapted to provide equal rated response of said controlled element for both said different settings of said selective means, and means operable to inhibit change in the setting of said selective means after initial setting thereof in one manneror the other.

' ll. A circuit protective device including a pair of contacts and operating mechanism therefor including a con-V trol bimetal and electric heating means therefor to render the control birnetal responsive to electric loading in the protected circuit, an ambient temperature compensating bimetal, and an unitary selector adjustable through a first range to determine the control point at which said control bimetal causes operation of said contacts, said selector being adjustable through a different range to cause cooperation of said ambient temperature compensating bimetal vvithV said control bimetal andrto determine the response point at which said control bi causes operation of the contacts.

l2. A circuit protective device including a pair of contacts and operating mechanism therefor including a current-responsive thermal element, an ambient temperature compensating element, and means having a calibrated scale and being adjustable through a range and cooperable directly with said mechanism to determine the control point at which said thermal element causes operation of said contacts, selective means adjustable to disable the direct cooperation of said adjustable means and said mechanism and concurrently to cause cooperation or said'ambient temperature compensating element and said mechanism, and means having another calibration scale and being adjustable through a range and cooperable with said ambient temperature compensating element to determine the response point at which saidV thermal element and said ambient temperature clement jointly cause operation of the contacts.`

13. A load responsive device including an enclosure containing a load responsive element and control mechanism therefor including a current-responsive thermal element inV control relation to said load-responsive element, an ambient temperature compensating element, and an unitary selector having a portion accessible externally of said enclosure, said selector being settable in direct cooperative relation to said mechanism, having a first calibration scale and being adjustable through a lirs't range to determine the point at which said load responsive element operates under control of said thermal element, said selector being differently settable to eliminate said direct cooperation with said mechanism and to cause cooperation of said ambient temperature compensating element With said mechanism, said unitary selector having a second calibration scale and being adjustable through a second range when set differently as aforesaid to determine the response point at which said thermal element and said compensating element jointly cause operation of said load-responsive element.

Y 14. A circuit protective device including a pair of contacts and operating mechanism therefor including a plurality of current-responsive thermal devices in control relation to said contacts and each current-responsive devicehaving means for heating thereof byra respective circuit of the protected device enabling operation of the contacts in response to any one or all of said devices, an ambient temperature compensating bimetal, and means including a selector settable to cause cooperation between said compensating bimetal and said devices in effecting overload tripping of said contacts and said selector being settable otherwise to establish control of said operating mechanism by said current-responsive thermal devices for operation of said contacts in a manner to eliminate said cooperation, said last-named means providing equal ratings of the protective device in both compensating and uncompensated settings of said selector.

15. A load-responsive device including a controlled element, a plurality of control thermal elements for the controlled element, each thermal element having heating means separately connectable to the respective circuits of a load device enabling operation of the controlled element in response to any one orV all of said control elements, an ambient temperature compensating thermal element, and means including a selector settable in one manner to cause cooperation between said compensating element and said control thermal elements in controlling said controlled element, said selector being settable otherwise to establish control of said control thermal elements over said controlled element in a manner to eliminate said cooperation, said load-responsive device having means providing equal load ratings in both said settings.

16. A circuit protective device including a pair of contacts and operating mechanism therefor including a plurality of control bimetals each having heating means separately connectable to a respective circuit of the protected device, and said mechanism including a mechanical connection between said bimetals and said contacts enabling operation of the contacts in response to any one or all of said control bimetals, an ambient temperature compensating bimetal, and means including a selector settable in one manner to cause cooperation between said compensating bimetal nd said control bimetals in relation to said mechanical connection and said selector being settable otherwise to establish control of said control bimetals over said contacts in a manner to eliminate said cooperation,- said selector being adjustable through a range of positions in each selected setting thereof to cause operation of said contacts in response to said bimetals at any adjusted load level.

17. A circuit protective device including a pair of contacts and operating mechanism therefor including a plurality of control bimetals each having heating means separately connectable to respective circuit of the protected device, and said mechanism including a mechanical connection between said bimetals and said contacts enabling operating of the contacts in response to any one or all of said control bimetals, an ambient temperature compensating bimetal, and means including a selector settable in one manner to cause cooperation between said compensating bimetal and said mechanism to modify the control elfect of said control bimetals and said selector being settable otherwise to eliminate said cooperation, said selector being adjustable through a range of positions in each selected setting thereof to cause operation of said contacts in response to such control bimetals at any level in a range of electrical conditions, and stop means coacting with said selector, said stop means being ettective when in assembled position for preventing said selector from operating out of either selected range of adjustment.

18. A load control relay for protecting a polyphase load including a pair of control contacts, a plurality of control bimetals each having electrical means for heating thereof and a respective connection for each of the phases of the protected load, and a mechanism connecting said bimetals to said contacts for control of the contacts by any or all said bimetals in the event of phase failure and in the event of overload, said mechanism including an adjustable stop, an ambient temperature compensating T0 bimetal carried by said stop and a selector 'alternatively settable' for direct coaction with said adjustable stop and settable differently for coaction with said stop only via said compensating bimetal.

19. A load control relay including a pair of control contacts, a plurality of control bimetals each having heating means and a respective connection for each of the phases of the protected load, and a mechanism connecting said bimetals to said contacts for control of the contacts by any one of said control bimetals in the event of phase failure and by all of said bimetals in the event of overload, said mechanism including an adjustable stop member, an ambient temperature compensating bimetal carried by said stop member, and a selector alternatively settable for direct coaction with said stop member and settable differently for coaction with said stop member only via said compensating bimetal, said selector being adjustable through a range of positions in each of the aforementioned settings yand effective to determine the contact-operating level in a range of load levels at which said contacts are tripped under bimetal control.

20. A circuit protective device including a pair of contacts and operating mechanism therefor including a plurality of control bimetals each having heating means separately connectable to a respective circuit of the protected device, and said mechanism including a mechanical connection between said bimetals and said mechanism enabling operation of the contacts in response to any one or all of said control bimetals, an adjustable stop member cooperable with said mechanism for determining the load level of contact operation, said stop member having a first rigid cam-following portion and said stop member having a temperature-compensating bimetal one portion of which constitutes a second cam following portion, and a selector adjustable to two ranges of positions and having a cam portion cooperable with said irst cam-following portion of the stop member and having a second cam cooperable with said second cam-following portion in the other range, said selector being effective to cause contact operation under control of said control bimetals at any load level within a range of levels, selectively with ambient temperature compensation or without ambient temperature compensation.

2l. A load responsive device, including a controlled element and control mechanism therefor, said control mechanism including a current-responsive bimetal, an ambient temperature compensating bimetal, selective means settable in one manner to impose the inuence of said compensating bimetal on said mechanism and thereby to modify the control effect of said current-responsive bimetal, and said selective means also being settable in another manner and at the same load-responsive rating to establish control of said controlled element by said current-responsive bimetal andv to eliminate said imposed iniluence, and locking means coacting with said selector for preventing inadvertent operation of the selector out of either selected setting.

22. A load-responsive device, including a controlled element and control mechanism therefor, said control mechanism including a current responsive bimetal, an ambient temperature compensating bimetal, selective means settable in one manner to impose the iniluence of said compensating bimetal on said mechanism and thereby to modify the control effect of said current responsive bimetal, and separate adjustment devices for establishing the calibration of the current responsive bimetal, one of said adjustment devices establishing the calibration of the current responsive bimetal when the selective means imposes the intluence of the compensating bimetal on the control mechanism, the other of said adjustment devices establishing the same calibration of the current responsive bimetal when the selective means is set to eliminate the inuence of the ambient temperature compensating bimetal.

erases 23'. A load-responsive device, including a controlled elemenLa thermal load-responsive element, selective reaction means, and a mechanism operated by said loadresponsive element and reacting against said selective reaction means to operate said controlled element, and an ambient temperature compensating bimetal, said selective reaction means having two contrasting settings and acting in both settings to provide reaction for said mechanism to enable said load-responsive element to operate said controlled kelement at the same calibrated rating in both settings, said ambient temperature compensating bimetal being included in said mechanism in only one of said settings and being excluded from said mechanism in the other of said settings.

24. 'A load responsive device in accordance with claim 23 wherein said selective reaction means includes a range of adjustment in each of said settings to modify the operation of said controiled element by said thermal loadrcspcnsive element over the same calibrated range or load ratings.

25, A load-responsive device, including a pair of contacts, a Current-responsive bimetal, selective reaction means, and a mechanism operated by said current-responsive bimetal and reacting against said selective reaction means to operate said contacts, and an ambient temperature compensating bimetal, said selective reaction means having two contrasting settings and acting in both settings to provide reaction for said mechanism to enable said current-responsive bimetal to operate said contacts at some critical load level, said ambient temperature compensating bimetal being included in said mechanism in one of said settings and being excluded from said mechanism in the other of said settings, said selective reaction means being adjustable over the same range of rated currents in each of said settings to cause operation of the contacts at any selected rated current whether set for operation with ambient temperature compensation or set for uncompensated operation.

26. A polyphase load-responsive device, including a controlled element a current-responsive bimetai for each phase of a polyphase circuit, selective reaction means, and a mechanism operated by any or all of Said currentresponsive bimetals and reacting against said selective reaction means to operate said controlled element either 12. in response to an overload or in response to phase failure,` and an ambient temperature compensating bimetal, said selective reaction means having two contrasting Vsettings and acting in both said settings to provide reaction for said mechanism to enable said current-responsive bimetals individually or in combination to operate said controlled element at the same rating in either of said two settings, said ambient temperature compensating bimetal being interposed between said mechanism and said selective reaction means in one of Said settings and said mechanism coacting directly with said selective reaction means in the other of said settings.

27. A load-responsive device in accordance with claim 26 wherein said selective reaction means. includes the same ranges of calibrated adjustment in each of its said contrasting settings to adjust the device for dilferent values of current within a range of current values.

28. A load-responsive device, including a controlled element, a current-responsive bimetal, an operating mechanism interconnecting said current-responsive bimetal and said controlled element, an ambient temperature compensating bimetal, and selective means imposing the iniluence of said ambient temperature compensating bimetal on said mechanism or, selectively, eliminating said inuence, said selective means being adapted to establish substantially equal rated load-responsive levels in the alternative settings of said selective means.

References Cited in the tile of this patent UNlTED` STATES 'PATENTS 

